A vehicle wheel normally comprises a pneumatic tire supported upon a wheel rim. The wheel rim usually includes a pair of axially spaced apart tire seats against which the beads of the tire are seated in use.
In between the tire seats of a one piece wheel, the wheel rim usually includes a well which, during fitting and removal of the tire, receives the beads of the tire to enable them to be passed over the tire seats.
In the event of a tire puncture, whilst the wheel is rotating (herein referred to as a “runflat operation”), it is possible for the tire, if sufficiently deflated, to come off of the wheel rim due to the tire beads entering the well. If this happens, steerage control of the wheel, and hence the vehicle, is lost.
It is known to provide a runflat assembly which during fitting of a tire on a wheel rim, are fitted to block-off the well and thereby prevent the beads of the tire entering the well.
It is important, once a runflat assembly has been fitted, that it does not become loose within the tire, particularly in the event of the deflation of the tire. Also, when deflation has occurred, it should be sufficiently robust to support the tire beads and prevent them from entering the well or deforming the runflat assembly.
These requirements necessarily mean that the runflat assembly has to be a good fit within the well of the wheel rim.
Unfortunately, there are a large number of different designs/shapes of wheel rims for vehicles, and so usually specific runflat assemblies are tailor made for particular designs of wheel rims.
In addition to the variety of designs/shapes of wheel rims, the materials from which the wheel rims are made can vary also. For example, wheel rims are commonly made from pressed steel or cast from a suitable alloy. This means that the runflat assemblies also have to be tailor made to accommodate the different materials from which the wheel rims are made.
It is not necessary to provide a well between the tire seats of two piece and multipiece wheels, because a tire is fitted to the wheel rim of such a wheel before the components of the wheel are secured together.
Multipiece wheels are primarily used in heavy duty and/or military applications. In such applications there is often a requirement for the vehicle to be run with tires at low pressures in order to obtain extra traction and/or flotation when required, e.g. in sand (military desert applications) or muddy conditions.
These vehicles are often fitted with a Central Tire Inflation System so that the tires can be significantly reduced in pressure and then re-inflated whilst on the move.
When the tires are fully inflated, the beads of the tire are retained in position, against the tire seats, by the pressure of the air within the tire. However, when the tires are run at a low pressure, there is a risk that the tire beads will move inwards, towards one another, across the wheel rim because the air pressure within the tire is not sufficient to retain the tire beads in position.
This creates a similar situation to a blowout, because the tire will instantaneously, and fully, deflate.
When this occurs the Central Tire Inflation System becomes ineffective and the tire cannot be re-inflated without removal from the vehicle.
An additional hazard, especially when the tire is used on sand, mud or water, is that sand/mud/water will get into the tire. This means that the tire must be completely removed from the wheel and cleaned before it is re-fitted and re-inflated.
It is known to provide a beadlock that is fitted around the wheel rim of a multipiece wheel between the beads of a tire and thereby retain the beads of the tyre tire spaced apart from each other, even when air pressure in the tire is reduced.
A beadlock can be fitted to a two piece or multipiece wheel, whereas it cannot be fitted to a single piece wheel provided with a well. This is because the provision of the beadlock would make it impossible to fit a tire to the single piece wheel.
The beadlock is fitted to the wheel so that it is a tight fit between the inner sections of the tire's beads, and it is usually fitted under pressure. The beadlock improves traction in extreme conditions because it helps to prevent the tire from slipping around the wheel under traction, and during braking conditions.
Known beadlocks are positioned between the beads of a tire before the tire is fitted to a two piece or multipiece wheel. They are often made of either a rubber or plastic ring, and are difficult to fit, having to be twisted and/or compressed to be able to be positioned inside a tire. During fitting of the tire, the tire, with a beadlock in position, is put over the wheel rim, and the complete assembly is forced down over the rim using a press.
This means that the beadlock must be tailor made to fit a particular tire and a particular wheel rim. This is because it is not possible to adjust the beadlock once it is fitted to a wheel, with a tire.